Generally, a refrigeration system of an air conditioning apparatus performs cooling and heating operations in such a way that the air conditioning apparatus absorbs heat from the air in a space to be air conditioned and discharges the heat outside the space, or the air conditioning apparatus absorbs heat from the outside air of the space to be air conditioned and supplies the heat into the space, by using the phase change of refrigerant.
The refrigerant is circulated in a circulation cycle comprised of evaporation—compression—condensation—expansion—evaporation during the cooling operation, while the refrigerant is circulated in a circulation cycle comprised of evaporation—expansion—condensation—compression—evaporation during the heating operation.
Such a refrigeration system of an air conditioning apparatus commonly includes a cooling system which is designed to lower a temperature of air in a space to be air conditioned (because the space to be air conditioned is generally a room, the space will be referred to as a room while the outside of the space to be air conditioned will be merely referred to as the outside of the room hereinafter, for the sake of convenience in explanation), a heating system which is designed to raise a temperature of air in the room, and a cooling and heating system which is designed to lower or raise a temperature of air in the room according to a user's selection.
A conventional refrigeration system includes an indoor unit installed in the room, an outdoor unit installed outside the room, a compressor which draws refrigerant in a state of lower temperature and lower pressure, compresses the refrigerant under the adiabatic condition to cause the refrigerant to have higher temperature and higher pressure, and discharges the refrigerant in the state of higher temperature and higher pressure, an expansion unit which allows for expansion of the refrigerant in a state of higher temperature and higher pressure under the adiabatic condition to cause the refrigerant to have lower temperature and lower pressure, and discharges the refrigerant in the state of lower temperature and lower pressure, a piping to connect the indoor unit, the outdoor unit, the compressor and the expansion unit to each other to allow the refrigerant to be circulated in a predetermined circulating path, various sensors provided at predetermined positions to monitor a temperature, a pressure and the like of the refrigerant, and a control unit to allow electricity to be supplied to the components such as compressor and the sensors and controls operations of the components such as the compressor, based on information received from the sensors. The refrigeration system further includes valves to change a circulating path of the refrigerant.
An operation of cooling a room by a cooling system or a heating system, and an operation of heating a room by a heating system or a cooling and heating system will now be described in detail.
In a cooling operation, liquid refrigerant in a state of lower temperature and lower pressure, which is introduced into the indoor unit, and then discharged to the compressor. The refrigerant in the state of lower temperature and lower pressure is compressed in the compressor, resulting in the refrigerant in higher temperature and higher pressure, and the refrigerant in higher temperature and higher pressure is discharged as gaseous refrigerant. The gaseous refrigerant in the state of higher temperature and higher pressure, which is discharged from the compressor, is introduced into the outdoor unit, and then condensed into liquid refrigerant in a state of higher temperature and higher pressure while radiating heat outside the room. The condensed liquid refrigerant is discharged to the expansion unit. The liquid refrigerant in a state of higher temperature and higher pressure, which is introduced into the expansion unit, is expanded, resulting in liquid refrigerant in a state of lower temperature and lower pressure, and then discharged to the indoor unit. As such, the refrigerant is circulated in the circulating cycle in the above-mentioned manner.
In a heating operation, gaseous refrigerant in a state of higher temperature and higher pressure, which is introduced into the indoor unit, is condensed into liquid refrigerant in a state of higher temperature and higher pressure while radiating heat to the room, and then discharged to the expansion unit. The liquid refrigerant in the state of higher temperature and higher pressure, which is introduced into the indoor unit, is expanded, resulting in liquid refrigerant in a state of lower temperature and lower pressure, and then discharged to the outdoor unit. The liquid refrigerant in the state of lower temperature and lower pressure, which is introduced into the outdoor unit, evaporates while absorbing heat from the outside air of the room, resulting in gaseous refrigerant in a state of lower temperature and lower pressure, and then discharged to the compressor. The gaseous refrigerant, which is introduced into the compressor from the outdoor unit, is compressed into gaseous refrigerant in a state of higher temperature and higher pressure, and then discharged to the indoor unit. As such, the refrigerant is circulated in the circulating cycle in the above-mentioned manner.
In the above conventional refrigeration system of air conditioning apparatus, the refrigerant into the compressor and the refrigerant discharged from the compressor must be maintained in a preset range in order to execute appropriate cooling and heating operations in the optimal circulation cycle without possible damage to the compressor.
It is preferable to control a temperature of the refrigerant, which is introduced into the compressor, to be slightly higher than that of a saturated refrigerant in which gaseous refrigerant and liquid refrigerant exist together, thereby allowing only gaseous refrigerant to exist in the compressor. This is because a compression capability of the compressor is lowered and the components of the compressor are damaged in a case that the liquid refrigerant is introduced into the compressor. Furthermore, when a temperature of the refrigerant, which is introduced into the compressor, is excessively raised compared to that of the saturated refrigerant in which gaseous refrigerant and liquid refrigerant exist together, the components of the compressor are deteriorated, thereby causing a service life and compression efficiency of the compressor to be drastically shortened and lowered.
Of the above problems, the former problem can be overcome by a simple method of supplying gaseous refrigerant separated through a gas-liquid separator to the compressor. The latter problem can be overcome by a method of lowering a temperature of refrigerant introduced into the compressor to prevent a temperature of the refrigerant from excessively rising than a temperature of the saturated refrigerant in which gaseous refrigerant and liquid refrigerant exist together, thereby lowering a compression load of the compressor, as disclosed in Korean Patent Application Nos. 2000-56277, 2000-56278 and 2000-56279.
Meanwhile, when a pressure of refrigerant, which is introduced into or discharged from the compressor, is excessively lowered, or an outside temperature of the compressor is excessively lowered, there are various problems, such as condensation on the compressor and malfunction of cooling and heating operations. However, methods of solving these problems are not proposed in any documents.